1. Field of the Invention
The present invention relates to a torque rod for use in an engine mount for a motor vehicle.
2. Description of the Related Art
It is already known to isolate vibration by letting the whole of a torque rod, which comprises an arm portion and bushings provided at each end in the longitudinal direction of the arm portion, function as a dynamic damper. There is also known the art that the arm portion is formed integral with a ring portion which surrounds the bushing, and the arm portion and the ring portion are made of resin so as to reduce weight. By the way, mass as the dynamic damper is decreased by being made of resin, so that resonance frequency becomes higher. Therefore, there is disclosed another torque rod that weight (mass) is mounted on the arm portion to adjust the resonance frequency to resonate at comparatively low frequency of about 100 Hz for example (see a patent reference 1).
Patent reference 1: Japanese patent laid-open publication No. H08-233030.
Incidentally, in the case where the weight is mounted on the arm portion as disclosed in the above prior art, it will take time and effort and increase in assembling man-hour. Also, in this case, since the arm portion is bent repeatedly by vibration, there is a possibility of disengagement of the weight in the long term use which is attached externally, thereby making an improvement in durability difficult. If the weight is integrally embedded in the rubber bushing, there is a possibility that spring characteristics of the rubber bushing is influenced so as to have the vibration isolating property varied. In addition, since the weight projects outwardly from the arm portion by being attached externally, it is essential to consider the layout not to come into contact with other neighboring parts.
It is therefore an object of the present invention to improve the durability by attaching the weight in such a way as not to be out of place through the long term use, and to make the layout easy without exerting an influence upon the spring characteristics of a principal spring section of the rubber bushing and without substantial external projection of the weight.